Drug resistant malaria kills millions annually. Reversing horrific trends in incidence and mortality requires a balanced approach in vaccine and drug research, as well as field based efforts to control vector populations and infection rates. Current and future treatment of the many different strains of drug resistant malaria that now exist requires a more complete understanding of multiple genotypes and phenotypes. We must not be lulled into a false sense of (temporary) security provided by current artemisinin (ART) based therapies; black market ART is already circulating and generating ART resistance. The struggle against drug resistant malaria is ongoing and must be met continuously; else we have learned nothing from the past 50 years while watching CQ and other drugs fail. We must stay ahead of the resistance curve and define molecular mechanisms that guides ongoing drug and vaccine research. Our laboratory has helped to lead the field in molecular level analysis of PfCRT and PfMDR1 proteins using heterologous expression systems. In this competitive renewal period we will: Aim 1) Continue to define binding functions of PfCRT isoforms via heterlogous expression in yeast and analysis of purified membrane, ISOV, and PL preparations harboring these proteins. We will use recently developed techniques and chemical probes for drug, amino acid, and ion binding and transport. We will also synthesize additional probes (e.g.,AzB-MQ, AzBCQ side chain length variants, AzB-QN) for PfCRT function. These probes will also be used in Aim 3. Aim 2) Continue to define drug transport functions of PfCRT isoforms using ISOV and PLs and radio labeled and fluorescent (e.g. NBD CQ) probes. We will also synthesize additional probes (e.g., NBD-MQ, NBD-QN) using previously synthesized intermediates and similar chemistry relative to successful synthesis of NBD-CQ. Aim 3) Test hypotheses for function of PfMDR1 following a similar approach, and also using high throughput plate based ATPase assays we have developed and published [93, 93B]. We will investigate the unusual (relative to other ABCB transporters) drug - influenced communication between the two symmetrical halves of PfMDR1 [93]. We will analyze binding, transport and ATPase properties of ISOV and PLs harboring known ratios of various PfCRT and PfMDR1 proteins to test for interactions between the two transporters.